H-23 parallelDrum Jul64

This document is the Instruction Manual for the Digital Equipment Corporation (DEC) Type 23 Parallel Drum, copyrighted 1964.

Purpose and Function: The Type 23 Parallel Drum serves as an auxiliary data storage device for the PDP-1D computing system, facilitating time-shared use of the computer. It provides data storage and retrieval, and can simultaneously read and write information in a "swap" or data exchange operation.

Key Specifications and Capabilities:

• Capacity: 32 fields, each storing 4096 words. Each word consists of 18 information bits plus an odd parity bit (19 bits total written on drum).
• Performance: Transfers 1 to 4096 words at a rate of 8.5 microseconds per word. A full 4096-word transfer or exchange takes approximately 35 milliseconds.
• Error Checking: Includes internal parity generation and checking during write/read cycles, and checks for data transmission timing errors. Error flags are set, and signals sent to the computer upon detection.
• Operation: Transfers are fully automatic, controlled by the computer program via IOT (Input/Output Transfer) instructions (DIA, DWC, DCL, DBA, DRA).

Physical Description: The unit is a 900-pound machine, constructed from two standard DEC computer cabinets (60-1/8" H x 47" W x 27-1/16" D). It features front-panel indicators and controls, with additional maintenance switches inside. Cooling is provided by fans with dust filters. The drum uses return-to-bias recording with aerodynamic read/write heads, requiring a 20-minute warm-up time for thermal stability before data transfers.

Maintenance: The manual outlines both preventive maintenance (mechanical checks, power supply checks, timing checks, and read/write head spacing/slice level adjustments) and corrective maintenance. Corrective procedures involve preliminary investigation, system troubleshooting (using diagnostic programs, signal tracing, and "aggravation tests" like vibrating modules to induce intermittent faults), circuit troubleshooting, repair, and validation testing.

In essence, the document is a comprehensive guide for personnel involved in the installation, operation, programming, and maintenance of the DEC Type 23 Parallel Drum, a high-capacity, high-speed auxiliary memory unit for the PDP-1D computer.